U.S. Pat. No. 5,702,735 to Martin et al., the entire disclosure of which is hereby incorporated by reference, provides an apparatus for molding polystyrene lens curves, i.e., front curves or back curves, which are used for subsequent molding of soft contact lenses. The apparatus is designed to provide superior heat conduction capacity so as to minimize the molding cycle time, while simultaneously producing uniformly precise and accurate optical quality surfaces. Molten polystyrene is provided via a hot runner system to a plurality of mold cavities. In a mold used to make front curves, the convex surfaces of the mold provide the optical quality surfaces to the concave surfaces of the front curves produced thereby. The structural element which defines each convex surface includes a hollow cylindrical bushing and a removable power insert mounted therein, which may be changed so that the prescription strength of the contact lens to be formed by the lens curves may be varied. In a first embodiment, the power insert includes only a convex surface at its operational end. In a second embodiment, the power insert includes an annular flat surface surrounding the convex surface, defining at the junction therebetween a discontinuity of curvature, which imparts a sharp edge to the front curve formed thereby. Cooling water is pumped into the core of the inserts to cool the inserts during the molding process, which complicates the process of changing the inserts. The power insert may be constructed of various materials including pure steel, brass, copper chromium, or cobalt-nickel alloyed martensitic steel. The power insert may be coated with a surface layer of nickel phosphor or silicone oxide, or chrome nitride. These layers may be turned to their proper thicknesses and dimensions by diamond cutters, and they may be thermally hardened.
U.S. Pat. No. 4,565,348 to Larsen, which is also incorporated by reference, discloses another prior art approach to manufacturing lens curves. Pursuant to this prior art approach, the lens curves are molded as a set of eight lens curves carried on a frame in a 2×4 array. FIG. 3 of the Larsen patent illustrates a molded frame carrying a 2×4 array of concave front curves, while FIG. 5 therein shows a molded frame carrying a 2×4 array of back curves. The cluster assembly of the frame and lens curves is manufactured by injection molding the assembly as one piece with the lens curves being secured within an outer rectangular frame by small struts extending between the frame and the lens curves. The height of the frame is such that the surfaces of the lens curves are protected from scratching and mechanical damage during handling, and the frame in general has a shape facilitating stacking and handling. This prior art approach of molding such polystyrene lens curves in a cluster assembly typically takes approximately twenty-four (24) seconds, which is too long for the efficient production of such polystyrene lens curves.
In this prior art approach, complementary sets of front and back curves are used in the production of hydrogel contact lenses by molding a reaction mixture wherein the mixture is preferably dissolved in a non-aqueous, water-displaceable solvent. After a dosing step in which the front curves are substantially filled with the reaction mixture, the concave front curves are covered with the back curves in a manner in which no air bubbles are trapped beneath the back curves. Back curves are placed on the polymerizable mixture in the front curves as individual units; therefore, prior to this step, the back curves are separated from their frames by breaking or cutting. The back curves are preferably held by a mechanical device while they are separated from the frame which thereafter places the back curves on the front curves. The reaction mixture is then subjected to conditions whereby it polymerizes, e.g. irradiation with actinic visible or ultraviolet radiation, to thereby produce a polymer in the shape of the desired hydrogel lens. After the polymerization process is completed, the two lens curves are separated (called demolding); typically leaving the contact lens in the front curve, from which it is subsequently displaced. Typically the front and back curves are used once to mold a single contact lens. After the polymerization is complete, the diluent is displaced with water to produce a hydrated lens.
U.S. Pat. No. 5,782,460, and WO 98/42497 disclose a method of making hydrogel contact lenses by molding a material which has been polymerized but is at least partially uncrosslinked within reusable molds. Crosslinking of the polymer is by UV radiation; therefore, the mold consists of a UV-permeable material, such as quartz, or polymeric materials. One or more contact lenses can be molded in each mold tool.
U.S. Pat. No. 5,451,155 to Kok et al., the entire disclosure of which is hereby incorporated by reference, discloses an arrangement for manufacturing goods, such as compact discs, by injection molding, providing a vertical injection molding machine including two holders that support mold plates. The mold plates are adjustable with respect to each other between a first position, in which the molding plates define a cavity, into which material is injected by the injection molding machine during operation, so that the particular molded good is formed, and a second position, in which the molding plates have been moved some distance apart, while the formed good is being removed. On each side of the injection molding machine, transport devices are provided which move the holder and molding plates from a position located at some distance from the injection molding machine to a position suitable for cooperation with the injection molding machine. The transport devices and the holders are detachably coupled. It is also disclosed that a holder may be provided with a new molding plate at some distance from the machine while the machine is in operation. For exchanging the molding plates and holders, it is only necessary to discharge the holder supporting the molding plate used so far, and to move the new holder and molding plate into position. This type of exchange of molding plates provides for a quick and simple retooling while minimizing the downtime of the injection molding operation.
There is a need in the art to improve the molds and molding technology for making ophthalmic devices, particularly for ophthalmic devices with many stock keeping units (SKUs). The term “stock keeping units” refers to different devices, e.g. different products. For example, contact lenses having different powers, and/or cylinders and/or axis values each combination of which would represent a different SKU, each SKU being manufactured using different molds or a different orientation of the molds or different reactive mixtures within the molds.